A: Infrared Absorption 197M—

Test specimen— Transfer a quantity of finely powdered Tablets, equivalent to about 50 mg of cyclobenzaprine hydrochloride, to a small flask, add 10 mL of methylene chloride, swirl to dissolve, and filter. Evaporate the clear filtrate to about 5 mL, transfer to a suitable centrifuge tube, and add 1 to 2 mL of ether. Evaporate with the aid of a current of air to about 1 mL, and agitate until crystallization occurs. Wash the crystals with several portions of ether, and air-dry.

B: The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation, as obtained in the Assay.

Medium: 0.1 N hydrochloric acid; 900 mL.

Apparatus 1: 50 rpm.

Time: 30 minutes.

Procedure— Determine the amount of C20H21N·HCl dissolved by employing UV absorption at the wavelength of maximum absorbance at about 290 nm on filtered portions of the solution under test, suitably diluted with Dissolution Medium, if necessary, in comparison with a Standard solution having a known concentration of USP Cyclobenzaprine Hydrochloride RS in the same Medium.

Tolerances— Not less than 75% (Q) of the labeled amount of C20H21N·HCl is dissolved in 30 minutes.

Mobile phase— Prepare a suitable filtered and degassed mixture of water, acetonitrile, methanol, and methanesulfonic acid (48:28:24:0.2), and adjust with diethylamine to a pH of 3.6. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Dissolve an accurately weighed quantity of USP Cyclobenzaprine Hydrochloride RS in 0.1 N hydrochloric acid, and dilute quantitatively, and stepwise if necessary, with 0.1 N hydrochloric acid to obtain a solution having a known concentration of about 0.05 mg per mL.

Assay preparation— Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 10 mg of cyclobenzaprine hydrochloride, to a 200-mL volumetric flask, add 150 mL of 0.1 N hydrochloric acid, and shake by mechanical means for 30 minutes. Dilute with 0.1 N hydrochloric acid to volume, mix, and filter.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 290-nm detector and a 4.6-mm × 10-cm column that contains packing L1. The flow rate is about 1.5 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the capacity factor, k¢, for the analyte peak is not less than 2.0; the column efficiency determined from the analyte peak is not less than 1000 theoretical plates; the tailing factor for the analyte peak is not more than 2; and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 10 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the areas for the major peaks. Calculate the quantity, in mg, of C20H21N·HCl in the portion of Tablets taken by the formula: in which C is the concentration, in mg per mL, of USP Cyclobenzaprine Hydrochloride RS in the Standard preparation: and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.